<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>130布局的技巧</title>
	</head>
	<style>
		.outter {
			background-color: gray;
			width: 400px;
			height: 400px;
		}

		.inner {
			background-color: orange;
			width: 200px;
			height: 100px;
			/* magin 上下设0，左右auto就会水平居中*/
			margin: 0 auto;
		}
	</style>
	<body>
		<div class="outter">
			<div class="inner">inner</div>
		</div>
	</body>
</html>